Impact machine

ABSTRACT

The invention provides an impacting device capable of , crushing or drilling work with reduced noise or vibration, with high crushing efficiency, high energy efficiency, increased output and prolonged durability 
     A super magnetostrictive material ( 1 ) is arranged in the center of an exciting coil ( 4 ) to which a pulse voltage is applied, a rod ( 12 ) is arranged in tight contact with the front end of the super magnetostrictive material ( 1 ), a reaction-receiving plate ( 3 ) is provided in tight contact with the other end of the super magnetostrictive material ( 1 ), and a power unit ( 6 ) is provided for repeatedly applying a pulse voltage to the exciting coil ( 4 ).

TECHNICAL FIELD

The present invention relates to an impacting device that utilizes animpact action produced by magnetostriction.

BACKGROUND ART

Heretofore, in impact machines, such as a breaker for crushing concreteor a rock with impacts or a drill for drilling a rock with impacts, theimpacting device for imparting impacts to the impact-transmitting tool,a chisel or a rod, for example, has used blows of a piston operated byhydraulic or pneumatic force.

However, in the impacting device such as this, a shock wave (a stresswave, namely, an elastic strain wave) occurs in the impact-transmittingtool, as a result of a blow of the piston, and this shock wave travelstoward an object, which is thereby crushed and therefore the sound of ablow and the reaction and vibration resulting from acceleration of thepiston have been unavoidable.

When a shock wave is produced, it is necessary to follow a series ofprocesses: electric energy is changed into mechanical energy by a motor,the mechanical energy is changed into kinetic energy of the piston by ahydraulic pump, for example, and the kinetic energy is changed intostrain energy of the impact-transmitting tool by a blow of the piston,thus producing a shock wave. The energy efficiency has not been so high.

To make the piston having a large inertial resistance reciprocate athigh speed, the accelerating force by hydraulic or pneumatic pressurehas not been sufficient and there is a limit to increasing the number ofblows, so that it has been not easy to increase output.

It has been known that there is a best waveform of a shock wave adequatefor the crushing characteristics (penetration resistance) of eachobject. Unless the waveform of the shock wave is adequate, theimpact-transmitting tool is unable to attain sufficient penetration intothe object, reducing the crushing efficiency and increasing reflectionof the shock wave from the object which partly contributes to increasingeffects to the impacting device and reducing the durability of theimpact machine. To control the waveform of a shock wave, measures havebeen taken, such as changing the shape of the piston to suit an object,but changing the piston shape is troublesome indeed.

DISCLOSURE OF THE INVENTION

The present invention has been made to solve the above problems and hasas its object to provide an impacting device for crushing and drillingwith low noise and vibration, which features high crushing efficiency,improved energy efficiency, high output and prolonged durability.

In the impacting device according to the present invention, the aboveproblems have been solved by arranging a super magnetostrictive materialin the center of the exciting coil to which a pulse voltage is applied,arranging an impact transmitting tool in contact with the front end ofthe super magnetostrictive material, and placing a reaction-receivingplate in contact with the other end of the super magnetostrictivematerial.

Magnetostriction is a phenomenon whereby the outside diameter dimensionof a ferromagnetic body, such as iron, changes when it is magnetized. Incontrast to strain of magnetic metals, which is no more than 10⁻⁵ to10⁻⁶, magnetostrictive materials exhibit strain on the order of 10⁻³ bymagnetostriction.

In this impacting device, a pulse voltage is applied to an excitingcoil, and by an exciting current flowing in the exciting coil, the supermagnetostrictive material is given changes of magnetic field so that thesuper magnetostrictive material produces such magnetostriction as togive a desired impact waveform. The impacting device transmits theshockwave through the impact-transmitting tool to an object, which isthereby crushed.

The impacting device according to the present invention convertselectric energy directly into strain energy and therefore has a highenergy efficiency ratio. And, because it does not require hydraulicequipment, hydraulic piping and complicated mechanical devices, such asa hydraulic striking mechanism, this impacting device makes it possibleto simplify the impact machine.

To make the impact-transmitting tool penetrate into an object, such as arock, with energy of a shock wave, it is necessary to maintain thedisplacement speed higher than a certain speed and longer than a certainperiod of time. Objects of rock and stone to be crushed are diverse inphysical properties and therefore they have various levels ofpenetration resistance. To ensure an amount of penetration greater thana certain value and to limit required power to a certain value or less,based on the facts that strain by magnetostriction is proportional tothe strength of a magnetic field, namely, the magnitude of an excitingcurrent and that the temporal change rate of strain is equal todisplacement speed, a pulse voltage is repeatedly applied to theexciting coil such that the exciting current of the exciting coilincreases with passage of a voltage-applied time and after reaching adesired maximum value, suddenly drops to zero. Consequently, the supermagnetostrictive material reaches desired displacement and displacementspeed in its deformation by magnetostriction. The pulse width at thistime is suitably selected from a range of several tens of μs up toseveral hundreds of μs, while the pulse interval is suitably selectedfrom a range of several ms up to several hundreds of ms.

When carrying out penetration of the impact-transmitting tool, theleading end of it is preferably in contact with an object. If theleading end of the impact-transmitting tool is not in contact with theobject, the shock wave returns as a tensile stress wave through theimpact-transmitting tool, making it impossible to effectively transmitenergy to the object. For this reason, it is necessary to have the wholeimpact-transmitting tool statically pressed against the object.

If a pulse voltage is applied to the exciting coil such that theexciting current of the exciting coil increases with passage of thevoltage-applied time, and after reaching a desired maximum value,maintains the maximum value for a specified time, so long as theexciting current maintains a fixed value, the super magnetostrictivematerial is prolonged and the impact-transmitting tool can be pressedagainst the object. The time for maintaining the exciting current at afixed value is suitably selected from a range less than several tens ofms.

To make effective use of a shock wave for penetration work of theimpact-transmitting tool into the object, it is important to minimizethe occurrence of reflected waves.

If a pulse voltage is applied to the exciting coil such that theexciting current of the exciting coil increases in proportion to anelapsed time squared or approximately as a logarithmic function duringpassage of a voltage-applied time from the initial value to the maximumvalue, then the occurrence of reflected waves can be reduced.

If a detection coil is provided adjacent to the exciting coil and if, onarrival of a reflected wave at the super magnetostrictive material fromthe impact-transmitting tool, changes in the current or voltage producedby magnetostriction are measured by the detection coil and the waveformof the reflected wave is detected by a detection unit and the magnitudeof an incident wave in the penetration process of theimpact-transmitting tool into the object is adjusted according to thereflected wave, then the occurrence of reflected waves can be reduced,which makes it possible to improve the penetration efficiency anddecrease vibration and reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of a breaker using an impactingdevice according to an embodiment of the present invention;

FIG. 2 is a schematic illustration of a breaker having a detection unitof reflected waves according to another embodiment of the presentinvention;

FIG. 3 is a schematic illustration of a drill using an impacting deviceaccording to a further embodiment of the present invention;

FIG. 4 is a graph showing a relation between penetration amount andpenetration force;

FIG. 5 is a graph showing a waveform of an incident wave;

FIG. 6 is a graph showing an example of a waveform of an excitingcurrent,

FIG. 7 is a graph showing another example of a waveform of an excitingcurrent;

FIG. 8 is a graph showing yet another example of a waveform of anexciting current;

FIG. 9 is a still further example of a waveform of an exciting current;and

FIG. 10 is a block diagram of a special waveform output power supply.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a schematic illustration of a breaker using an impactingdevice according to an embodiment of the present invention. FIG. 2 is aschematic illustration of a breaker having a detection unit of reflectedwaves according to another embodiment of the present invention. FIG. 3is a schematic illustration of a drill using an impacting deviceaccording to a further embodiment of the present invention.

In a breaker B in FIG. 1, a super magnetostrictive material 1 isarranged in the center of an exciting coil 4 provided in a casing 5. Achisel 2 as an impact-transmitting, tool is arranged in contact with thefront end of the super magnetostrictive material 1, and areaction-receiving plate 3 is placed in contact with the other end ofthe super magnetostrictive material 1. In crushing work, the breaker Bis given a thrust T by a thrust unit (not shown), the tip of the chisel2 is pressed against an object 7, and a power unit 6 applies a pulsevoltage to the super magnetostrictive material 1.

In crushing work, the breaker B is given a thrust T by a thrust unit(not shown), the tip of the chisel 3 is pressed against an object 7, anda power unit 6 applies a pulse voltage to the super magnetostrictivematerial 1.

When a pulse voltage is applied to the exciting coil 4, the supermagnetostrictive material 1 is given changes in magnetic field by anexciting current flowing through the exciting coil 4, and suchmagnetostriction occurs as produces a desired impact waveform. The shockwave is transmitted to the object 7 through the chisel 2 placed incontact with the front end of the super magnetostrictive material 1, andthe object is crushed by the shock wave.

As the thrust unit, any of those types which have been used with theconventional impact machine, such as a gravity, hydraulic, pneumatic,mechanical or manual type, can be used. To protect the supermagnetostrictive material 1, it is preferable to install an non contactstriking preventive means that turns on or off the power unit 6 bydetecting the thrust of the thrust unit.

In a breaker B in FIG. 2, a detection coil 8 is provided between thesuper magnetostrictive material 1 and the exciting coil 4, and thedetection unit 9 detects the waveform of a reflected wave by measuringchanges in a current or a voltage generated by magnetostriction with thedetection coil 8 when the reflected wave coming from the chisel 2arrives at the super magnetostrictive material 1. The other componentsof this breaker are the same as those of the breaker in FIG. 1.

In a drill D in FIG. 3, a super magnetostrictive material 1 is arrangedin the center of an exciting coil 4 provided in a casing 5, and a rod 12as the impact-transmitting tool is arranged in contact with the frontend of the super magnetostrictive material 1. A bit 13 is attached tothe leading end of the rod 12. The drill D is equipped with a rotatingunit 11 and a flushing unit 15, the rod 12 is rotated by the rotatingunit 11 and the flushing unit 15 supplies a fluid for ejecting cuttings.

The operation of the impacting device will be described by referring tothe drill D in FIG. 3.

Magnetostriction is a phenomenon that the outside diameter dimension ofa ferromagnetic body, such as iron, changes when it is magnetized. Incontrast to magnetic metals, which show strain of no more than 10⁻⁵ to10⁻⁶, magnetostrictive materials exhibit strain on the order of 10⁻³ bymagnetostriction.

The super magnetostrictive material 1. undergoes magnetostriction andserves as a piston to strike the rod 12 and generates a shock wave.

When the rod 12 is sufficiently longer than the piston, the totalkinetic energy of the piston is transmitted as a shock wave to the rod12. The magnitude σ (stress) of a shock wave produced at this time isgiven by σ=(E/C)v where Young's modulus of the material of the rod 12 isdenoted as E, the speed of a shock wave that travels in the rod, namely,the speed of sound is denoted as C and the speed of displacement of theend face of the rod by a blow is denoted as v.

With ordinary drills, the magnitude of σ is about 200 MPa from thedurability of the rod and strain is about 10⁻³.

If the sectional area of the rod 12 is denoted as A, the load f of therod 12 by this shock stress σ is expressed by f=σA=(AE/C)v The quantity(AE/C) is called the specific impedance of the rod. If this specificimpedance is denoted as Z, the f can be expressed as f=Zv. In otherwords, the load f of the rod 12 is the product of the specific impedanceZ intrinsic to the rod 12 and the displacement speed v of the rod 12.The shock energy to be transmitted to the rod 12 is not completelyimparted to the rod 12, but part of the shock energy is lost byreflection that invariably occurs where the specific impedance Zchanges.

The reflectance R of this reflection is expressed by R=ΔZ/ΣZ by using adifference ΔZ and sum ΣZ of the specific impedances Z before and afterthe plane of reflection. The behavior of the shock wave that has arrivedat the leading end of the rod 12 is as follows. when the bit 13 does notcontact anything and remains a free end, because the specific impedanceZ of the object is 0, the load at the leading end is 0, soR=(0−Z)/(0+Z)=−1. The shock energy is not transmitted to the object atall. If the shock wave is a compressive stress wave, R=−1 and the signis changed and the shock energy is reflected 100% as a tensile stresswave.

On the other hand, when the bit 13 is in contact with an object withoutany deformation at all and forms a fixed end, the reflectanceR=(∞−Z)/(∞+Z)=+1. Because the displacement of the leading end of the bit13 is 0, no energy is transmitted to the object at all, and the load atthe leading end is twice as much as f by mutual superposition of anincident wave and a reflected wave, namely, 2f. Because R=+1 at thistime, a compressive stress wave is reflected 100% as a compressivestress wave.

It has been known that as the whole bit 13 is made to penetrate into anobject to be crushed, such as a rock with a static thrust, a fixedrelation F=Φ(u) is maintained between penetration amount u andpenetration force F as shown in FIG. 4 and that also when a dynamicthrust is used, this relation substantially remains intact. In thisrelation, the penetration force per unit of penetration amount, that is,dF/du is referred to as penetration resistance.

If the penetration resistance of the object 7 to the bit 13 is equal inmagnitude to the specific impedance Z of the rod 12, R=(Z−Z)/(Z+Z)=0, inother words, the reflection is 0. More specifically, all energy istransmitted to the object 7, and the load on the leading end of the bit13 at this time is equal to f. To be more specific, at the leading endof the bit 13, only when the penetration resistance is equal to theresistance while a shock wave is transmitted through the rod 12, 100% ofenergy is transmitted to the object 7. Or otherwise, 100% of energy isnot transmitted. When the penetration resistance is smaller than theabove-mentioned reflectionless impedance, the remainder of energy isreflected as a tensile stress wave, and when the penetration resistanceis larger than the reflectionless impedance, the remainder of energy isreflected as a compressive stress wave.

When the shock wave reaches the leading end of the bit 13 in contactwith the object 7 having a penetration resistance, the penetration ofthe bit 13 and the occurrence of a reflected wave from the shock wavetake place. As shown in FIG. 5, with a shock wave of an arbitrarywaveform, the load f appears to be constant for a very short time Δt(several μs for example). Suppose that the penetrating bit 13 is, asshown in FIG. 4, at the position a in the relation between thepenetration amount u and the penetration force F and that thepenetration force at this time is F₀=Φ(u₀). If the time Δt is small, themagnitude r of a reflected wave produced at the bit 13 can be regardedapproximately as r=F₀−f. The leading end of the bit 13 advances bymutual superposition of an incident wave and a reflected wave. Theadvancing speed of the bit 13 in this time Δt is v=(r−f)/Z from r−f=Zv,and therefore the advancing amount of the bit 13, that is, an increaseΔu in the penetration amount is obtained by Δu=(r−f)Δt/Z. On completionof this penetration, the magnitude of the penetration force hasincreased from F₀=Φ(u₀) to F₁=Φ(u₀+Δu).

By repeatedly performing the above procedure, with regard to anarbitrary incident wave, it is possible to know how the penetrationamount and the penetration energy to an object 7 to be crushed, whichhas a penetration resistance, change with passage of time.

From the above observation, it can be seen that to make the bit 13penetrate into an object 7 like a rock with energy, such as a shockwave, it is necessary for a displacement speed v higher than a certainspeed to be continued for a certain period of time from theabove-mentioned equations. such as f=Zv, Δu=vΔt.

The physical properties of objects 7 to be crushed, such as a rock. arediverse and therefore they have various levels of penetrationresistance. To ensure a penetration amount over a certain amount andlimit required power to a certain value or less, because strain bymagnetostriction is proportional to the strength of a magnetic field, inother words, the magnitude of an exciting current and the temporalchange rate of strain is equal to displacement speed v, as shown in FIG.6, a pulse voltage is repeatedly applied to the exciting coil 4 from apower unit 6 such that the exciting current of the exciting coilincreases with passage of a voltage-applied time and after reaching adesired maximum value, suddenly falls to zero. By this arrangement, adesired displacement and a desired displacement speed can be achieved indeformation of a super magnetostrictive material 1 by magnetostriction.The pulse width at this time is suitably selected from a range ofseveral tens of μs up to several hundreds of μs, and the pulse intervalis suitably selected from a range of several ms up to several hundredsof ms.

When carrying out penetration of the bit 13, the leading end of the bit13 is preferably in contact with the object 7. If the leading end of thebit 13 is not in contact with the object 7, a shock wave incident on theleading end of the bit 13 returns as a tensile stress wave into the rod12, so that the energy cannot be effectively transmitted to the object7. For this reason, it is required to have the whole rod 12 staticallypressed against the object 7.

As shown in FIG. 7, if a pulse voltage is applied to the exciting coil 4in such a way that the exciting current of the exciting coil 4, as itrises in a pulse waveform, increases with passage of a voltage-appliedtime, and after reaching a desired maximum value, while the excitingcurrent maintains the maximum value for a fixed period of time, thesuper magnetostrictive material 1 is prolonged, making it possible forthe rod 12 to be pressed against the object 7, so that an instantaneousthrust deficiency, which the thrust unit is unable to deal with, can becompensated. The time in which a fixed value is maintained may besuitable selected from a range of several tens of ms.

To make effective use of a shock wave for penetration work into theobject 7, it is important to minimize the occurrence of a reflectedwave. More specifically, to reduce the magnitude r of a reflected waveto zero, it is required to keep f=−F (the −sign indicates a compressivestress wave) from r=−F−f=0.

With an object 7 for which assumption can be made that F=Φ(u)=ku, we canderive dF=−df=kdu=(k/Z)fdt from v=du/dt=−f/Z. If f=f₀e^((k/Z)t), noreflected wave occurs. If the fact that the initial f₀ necessary for theinitial penetration and the penetration resistance of the object 7 to becrushed are not necessarily expressed correctly as F=ku is taken intoaccount, when a pulse voltage is applied to the exciting coil so thatthe exciting current of the exciting coil increases in proportion to anelapsed time squared (i=αt²) or approximately as a logarithmic functionof an elapsed time (i≈αe^(kt)) during passage of a voltage-applied timefrom the initial current value at rising of a pulse waveform up to themaximum value as shown in FIGS. 8 and 9, the occurrence of a reflectedwave can be minimized.

If a detection coil 8 is provided adjacent to the exciting coil 4, whena reflected wave returns from the rod 12 to the super magnetostrictivematerial 1, by measuring changes in current or voltage produced bymagnetostriction with the detection coil 8 to detect a waveform of thereflected wave with a detection unit 9 and by increasing or decreasingthe magnitude of an incident wave in the penetration process of the bit13 into the object 7 according to the reflected wave, reflected wavescan be reduced, making it possible to improve the penetration efficiencyand reduce vibrations or reactions.

To supply the exciting coil 4 with a pulse voltage as mentioned above, aspecial wave form output power unit 36 including a transformer 32, adiode rectifier 33, a high-frequency inverter 34 and a filter 35 shownin FIG. 10, capable of transforming an AC input 31 into the form of aspecial-waveform pulse is used as the power unit 6. The special waveformoutput power unit 36 controls an applied voltage so as to obtain a pulsecurrent of a desired waveform according to inductance of the electriccircuits and detection results by the detection unit 9 with respect tothe waveform of a reflected shock wave.

INDUSTRIAL APPLICABILITY

As is obvious from the above description, the impacting device accordingto the present invention directly converts electric energy into strainenergy and therefore has a high energy efficiency and does not requirehydraulic equipment, hydraulic piping and complicated mechanicaldevices, such as a hydraulic striking mechanism, this impacting devicecan simplify the impact machine.

It becomes possible to operate the impact machine at high speed byelectric pulse and more easily produce high output than in themechanical piston striking operation. Being capable of easy productionof a desired impact waveform, this impacting device improves penetrationefficiency and crushing efficiency.

This impact machine measures a reflected wave by deformation of thesuper magnetostrictive material, and reflects detection results in theoutput waveform, making it possible to reduce reflected waves, improvepenetration efficiency and decrease vibrations and reactions. Above all,because striking noise is eliminated, it is possible to provide a quiet,high-durability impact machine.

What is claimed is:
 1. An impacting device comprising: an exciting coilactuated by application of a pulse voltage; a super magnetostrictivematerial arranged in the center of said exciting, coil; animpact-transmitting tool in tight contact with a leading end of saidsuper magnetostrictive material; a reaction-receiving plate in tightcontact with the opposite end of said super magnetostrictive material;and a power unit for repeatedly applying to said exciting coil a pulsevoltage such that an exciting current of said exciting coil increases inproportion to an elapsed time squared or approximately as a logarithmicfunction during passage of a voltage-applied time from an initial valueto a maximum value.
 2. An impacting device according to claim 1, furthercomprising a detection unit having a detection coil provided adjacent tosaid exciting coil, wherein when a reflected wave returns from saidimpact-transmitting tool to said super magnetostrictive material, saiddetection unit detects a waveform of the reflected wave by measuringchanges in current or voltage by magnetostriction with said detectioncoil.
 3. An impacting device according to claim 1 wherein the excitingcurrent, after reaching the desired maximum value, suddenly falls tozero.
 4. An impacting device according to claim 3, further comprising adetection unit having a detection coil provided adjacent to saidexciting coil, wherein when a reflected wave returns from saidimpact-transmitting tool to said super magnetostrictive material, saiddetection unit detects a waveform of the reflected wave by measuringchanges in current or voltage by magnetostriction with said detectioncoil.
 5. An impacting device according to claim 1 wherein the excitingcurrent, after reaching the desired maximum value, maintains a maximumvalue for a specified time and then suddenly falls to zero.
 6. Animpacting device according to claim 5, further comprising a detectionunit having a detection coil provided adjacent to said exciting coil,wherein when a reflected wave returns from said impact-transmitting toolto said super magnetostrictive material, said detection unit detects awaveform of the reflected wave by measuring changes in current orvoltage by magnetostriction with said detection coil.
 7. An impactingdevice comprising: an exciting coil actuated by application of a pulsevoltage; a super magnetostrictive material arranged in the center ofsaid exciting coil; an impact-transmitting tool in tight contact with aleading end of said super magnetostrictive material; areaction-receiving plate in tight contact with the opposite end of saidsuper magnetostrictive material; and a detection unit having a detectioncoil provided adjacent to said exciting coil, wherein when a reflectedwave returns from said impact-transmitting tool to said supermagnetostrictive material, said detection unit detects a waveform of thereflected wave by measuring changes in current or voltage bymagnetostriction with said detection coil.
 8. An impacting deviceaccording to claim 7, further comprising a power unit for repeatedlyapplying to said exciting coil a pulse voltage such that an excitingcurrent of said exciting coil increases with passage of avoltage-applied time, and after reaching a desired maximum value,suddenly falls to zero.
 9. An impacting device according to claim 7,further comprising a power unit for repeatedly applying to said excitingcoil a pulse voltage such that an exciting current of said exciting coilincreases with passage of a voltage-applied time, and after reaching adesired maximum value, maintains a maximum value for a specified timeand then suddenly falls to zero.